1. Field of the Invention
This invention relates to a transmission system and a transmitting device, and more particularly to a transmission system that carries out control operations for recovering a fault which has occurred, thereby performing transmission control, and a transmitting device for carrying out control operations for recovering a fault which has occurred, thereby performing transmission control.
2. Description of the Related Art
Recently, the traffic of IP (Internet Protocol) packets is increased along with the increasingly widespread use of the Internet. Further, the data contents of the IP packets are more diversified, and in addition to conventional computer data, data of sounds, motion pictures and the like requiring real time properties are increased.
In line with the above circumstances, to shorten a time period for transferring IP packets, a layer 2 label switching technology of adding an address label to each IP packet has been proposed.
The label switching technology is a high-speed packet transfer technology which is capable of realizing the layer 3 communication between different networks, which has been conventionally realized by using routers, by directly connecting the networks to each other in the layer 2 without using an upper layer. For the label switching technology, a method called MPLS (Multi-Protocol Label Switching) has been developed.
In MPLS, all control operations are carried out by IP (Internet Protocol), and a label with a fixed length is added to each IP packet to enable the IP packet to be transferred throughout a network by the label. The MPLS method is based on the concept of a label path, and is largely different in characteristics from the conventional IP in that it is connection-oriented.
The method of fault recovery control of MPLS includes a global repair method and a local repair method. The global repair method is a path-end switching method for recovering from a fault at path ends (at the inlet (ingress) and outlet (egress) of an MPLS network), while the local repair method is a fault-end switching method for switching a local path where a fault has occurred to another at the ends of the local path (between routers close to a link where the fault has occurred). When a line fault or the like has occurred, the above recovery control operations are carried out to set a route for recovering the fault, thereby recovering from the fault.
However, in the above-described conventional fault recovery control performed by the global repair method, when a path having a fault is switched to a path for recovering the fault, load applied to the fault recovering path after completion of the switching has not been considered at all.
Therefore, there is a fear that traffic loads are concentrated on the fault recovering path, which causes biased traffic and degraded operating efficiency of the system.
On the other hand, in the conventional fault recovery control performed by the local repair method, a route bypassing the local path in which a fault has occurred is searched for at an end of the local path, and then the packet is transferred to the route, i.e. a path for recovering the fault. This search processing takes much time, and hence hinders realization of efficient high-speed transfer.